1. Field of the Invention
The invention relates to personal computer (PC) or workstation architecture particularly with respect to text and graphics displays on the monitor thereof. The invention specifically concerns the display of Japanese characters in a text mode and the support of standard EGA display modes for English and other western language text and EGA graphics.
2. Description of the Prior Art
Three different protocols are presently utilized for the generation of computer text and graphics on a monitor; viz., the EGA standard, the VGA standard and the Architecture Extended (AX) standard. The EGA standard, which was the first to be established, utilizes a digital EGA monitor that accepts digital video signals from the video controller. The EGA standard utilizes six bits of digital video to define 64 colors. Conversion circuitry in the EGA monitor transforms the digital video signals to the appropriate drive signals for the color gun system of the monitor. The EGA standard utilizes a resolution of 640.times.350 pixels in the text modes and the standard EGA monitor includes horizontal and vertical oscillators tuned to accept horizontal and vertical synchronization frequencies appropriate for this mode of operation. As is well known, such oscillators utilize phase locked loop circuitry capable of locking to the horizontal and vertical sync signals over narrow frequency ranges. The EGA standard utilizes a 9.times.13 pixel character matrix in text display modes.
Although the resolution of 640.times.350 pixels is adequate for the display of English language and other western language text as well as for some graphics modes, higher resolutions of, for example, 640.times.480 pixels is required for high resolution graphics displays. EGA systems that support text and high resolution graphics require the use of a multi-sync monitor. A multi-sync monitor contains a plurality of horizontal and/or vertical oscillators for synchronizing to the various horizontal and vertical sync frequencies required for the low to high resolution EGA modes and thus has the capability of displaying video at a plurality of horizontal and vertical sync frequencies. Present day EGA multi-sync monitors tend to be extremely expensive because of the complex plural synchronization requirements. Additionally, such monitors are not widely and commonly utilized and hence have not benefited from large scale mass production economies. The EGA system utilizes a standard EGA chip set and associated software.
In such systems, it is desirable to display Japanese fonts and characters on the monitor screen in text modes of operation. Japanese fonts include Kanji, Hirekana and Katakana. The Kanji character set includes over 8000 characters. These fonts are utilized for writing and processing Japanese text on a PC architecture computer. However, because of the complexity of Japanese characters compared, for example, to English alphabet characters, EGA text mode standards are inadequate to provide a display of clearly distinguishable and easily readable Japanese text. This inadequacy results primarily from the resolution and character matrix size utilized in the text mode of the EGA standard. It would be possible, however, to generate reasonable quality Japanese text on an EGA monitor utilizing an EGA graphics mode. Equipment operating in a graphics mode is generally slower than text mode oriented equipment. In a graphics mode, the screens of Japanese text would be generated at an inadequate speed to provide acceptable display performance in text oriented applications such as word processing.
The Architecture Extended (AX) standard was developed for providing high performance and high speed display of Japanese characters in a text mode of operation, thus providing adequate support for the generation and display of Japanese characters. The AX standard supports EGA modes (AX-EGA), so that both Japanese and English text can be displayed utilizing the same system. In the AX mode for the display of Japanese characters, a resolution of 640.times.480 pixels and a character matrix of 16.times.16 pixels is utilized to properly support the display of the complex Japanese characters. As previously described, the EGA text mode standard utilizes a resolution of 640.times.350 pixels. In order to support the diverse resolutions required in the Japanese AX mode and in the EGA English mode, a multi-sync monitor is required. Although multi-sync monitors can support most text and graphics modes, the multi-sync monitor is extremely expensive. Additionally, only the limited number of colors available under the EGA standard are displayed. It is appreciated that the AX mode utilizes the standard JEGA chip set (Japanese EGA).
The VGA standard was developed to provide significantly enhanced modes and capabilities with respect to the EGA system. The VGA protocol has substantially replaced the EGA system and is now utilized as the industry standard. EGA equipment is still, however, utilized and supported.
The VGA monitor is an analog monitor that receives analog video signals from the CPU. The VGA standard supports 256 simultaneous colors from a palette of 256K colors, and all text and graphics modes with resolution formats ranging from 320.times.200 pixels to 640.times.480 pixels. The VGA character matrix is 9.times.14 pixels. The VGA monitor is a "verisync" monitor in that the monitor supports numerous resolution formats without a plurality of horizontal and vertical oscillators as in the multi-sync monitor. The VGA monitor utilizes only one horizontal oscillator and only one vertical oscillator. The VGA standard supports the various text and graphics modes with plugable circuit boards within the CPU that provide logic and programming, in a well-known manner, such that the various required resolutions are properly effected by the VGA monitor. Logic, implementing clock alterations and pixel combinations and the like, effects the various modes.
Notwithstanding the enhanced capability of the VGA standard, the VGA monitor is significantly less expensive than the EGA monitor because of the analog video simplicity and the single horizontal and vertical oscillator requirements thereof. Additionally, since the VGA monitor is currently the most widely used type, large scale mass production has resulted in greatly reducing the price thereof. Thus, the VGA monitor is significantly less expensive than the EGA monitor and extremely more economical than the multi-sync EGA monitor.
Although the VGA standard supports all known graphics and English language text modes, the VGA system does not adequately support the display of Japanese text for the reasons discussed above with respect to the EGA standard. Thus, the current state of the art is that the AX-EGA standard exists for supporting Japanese text and EGA modes but requires an extremely expensive multi-sync EGA monitor. The industry standard VGA protocol provides enhanced capabilities and supports significantly more modes than the prior EGA standard, but is unsuitable for the display of Japanese text.